One form of filter device comprises a flat or areal carrier to which adsorber particles are fixed. The carrier forms a plurality of mutually adjacent layers which are fixed in a filter housing having an inlet for a gaseous medium to be filtered and an outlet for the filtered gaseous medium. The layers of the carrier are so arranged in relation to the inlet and the outlet of the filter housing that the gaseous medium to be filtered does not pass through or penetrate the layers but only flows along them and along the adsorber particles thereon. The layers are of a flat configuration and are assembled to constitute a rectangular parallelepipedic stack in the filter housing.
A filter device of generally similar kind is to be found in DE 40 39 951 A1 which refers to adsorber particles in the form of small cylinders which however are disposed in loose-fill form in the filter. In connection with loose-fill filters of that configuration, with adsorber particles in the form of small cylinders, it is stated therein that they cause the through-flow resistance, that is to say the resistance to the flow of gaseous medium through the filter, to become excessively high, if they are less than a given minimum size. Accordingly, that filter device preferably uses adsorber particles of spherical shape which are suitably fixed to a carrier.
U.S. Pat. No. 3,925,021 discloses a filter device in which carrier layers are connected to form a generally rectangular parallelepipedic stack by means of a plastic material forming at least a part of the filter housing.
A filter device with a flexible frame structure is to be found in DE 92 16 049 U1. That filter device is in particular an air filter for internal combustion engines, that is to say it is a particle filter and not an adsorber filter with absorber particles operative by virtue of an adsorption action.
EP 0 383 236 B1 discloses a filter device having a flat carrier folded in a zig-zag configuration. The carrier is gas-permeable because a gaseous medium to be filtered by the device has to pass through the carrier. Therefore, in order that the flow resistance through the filter device remains within suitable limits, it is necessary for the fold spacing between adjacent layers of the carrier not to be too small.
A filter device with a flat carrier which is folded in a zig-zag configuration is also to be found for example in German laid-open application (DE-OS) No 29 41 094. In this case also the carrier must comprise a gas-permeable material because the gaseous medium to be filtered passes through the carrier. The same consideration applies in regard to filter devices as are to be found for example in U.S. Pat. No. 3,651,659 or German laid-open application (DE-OS) No 25 12 659.
A filter device with a flat carrier comprising a gas-permeable material is also known for example from German laid-open application (DE-OS) No 24 06 243. In order to achieve the required level of stability in respect of shape in the case of that filter device, the carrier thereof is combined with a flat stabilization system.
EP0 045 516 B1 discloses a filter device with a flat carrier which can be folded together in a zig-zag configuration to form carrier layers, or in which the carrier is wound on to a gas-permeable tubular bar or mandrel in order to provide carrier layers in the manner of a spiral coil or winding. This arrangement however also involves a given minimum flow resistance in relation to the gaseous medium to be filtered because it is required to flow through the carrier which is folded in a zig-zag configuration or wound as a spiral coil. When such a filter device is used for example in combination with a fan assembly, that not inconsiderable flow resistance gives rise to the need for a corresponding level of drive power. That given minimum fan power in turn results in the development of a corresponding amount of noise which is perceived as being a nuisance for example in the fields of use such as vehicle heating, ventilation, air conditioning or like systems.
A filter device with a housing having a carrier providing a plurality of mutually adjacent layers fixed in a filter housing with an inlet and an outlet, with the layers being arranged in such a way that the gaseous medium flows along the layers as it passes through the housing is also to be found in GB-A-1 026 591. In that arrangement the carrier is wound on to a central bar or mandrel, thus affording mutually adjacent layers which form the round turns or windings of a spiral body. In that filter device the gaseous medium to be filtered thus does not flow through the carrier but along the turns or windings and the adsorber particles thereon, so that the flow resistance through the filter device is relatively low in comparison with filter devices in which the gaseous medium to be filtered is required to flow through the carrier. It has been found however that, when filter devices with a carrier wound in a spiral form of that kind are combined with fan devices, the vibration produced by the fan devices is picked up by the filter device and transmitted in unattenuated form or in an extreme situation even in an enhanced fashion, and that must be considered highly disadvantageous.
DE-A-43 39 025 discloses a method and an apparatus for cleaning polluted exhaust or waste air by means of heterogeneous catalysis. That apparatus can have a spiral winding comprising a non-metallic carrier material and an electrically conductive woven strip. That arrangement also provides for selective adsorption, besides a catalysis effect. In this case also however the spiral winding gives rise to the same problems, in regard to vibration and sound transmission, as in the case of the filter device disclosed in above-discussed GB-A-1 026 591.